A number of motion simulation systems or mechanisms are known with a restricted degrees of freedom. It is also known to produce mechanisms which provide motion in three degrees of freedom, viz. the axes of heave, pitch and roll.
For ease of convenience, pitch refers to the motion in which the moving platform rotates about its X-axis (transverse axis). Roll refers to the motion in which the moving platform rotates about its Y-axis (longitudinal axis). Yaw refers to the motion in which the moving platform rotates about its Z-axis (vertical axis). Surge refers to the translational motion of the moving platform along its Y-axis. Sway refers to the translational motion of the moving platform along its X-axis.
One of the motion simulators has been described in U.S. Pat. No. 3,295,224 (1967; re-issued as Re 27,051 in 1971) which describe a motion simulator consisting of a planar spatial frame connected to a fixed base frame and is defined by at least three stationary points on the grounded base. It is connected to six independent kinematic legs, these six legs are connected to both the base plate and top plate by universal joints in parallel located at both ends of each leg. The legs are designed with an upper body and lower body that can be adjusted, allowing each leg to be varied in length.
FIG. 1 shows the isometric view of the motion simulator described above. To achieve a single degree of freedom in the top frame all the actuators need to be actuated. The loads are directly on the actuator which would result in greater power rating for the actuators. For each individual moment (degrees of freedom) either (pitch, row, yaw, surge and sway), all the actuators need to be moved simultaneously with varying velocities, resulting in non utilization of alternative constant velocity actuators. In order to reduce the degrees of freedom for different applications, all six actuators have to be present.